If you're thinking of the political left and right, here's the explanation from Wikipedia:

«The terms Left and Right to refer to political affiliation originated early in the French Revolutionary era, and referred originally to the seating arrangements in the various legislative bodies of France, specifically in the French Legislative Assembly of 1791, when the moderate royalist Feuillants sat on the right side of the chamber, while the radical Montagnards sat on the left.»

Left comes from the Mid-English "lyft" and/or Middle Low German "lucht" which means "weak" or useless.

Right comes from the Mid-English "riht" and/or Old High German "reht" which generally mean "straight" or "rule".

Basically, most people's left hand is weak and useless and the right hand is the hand you use to do stuff, it is your strong hand, or your "ruling" hand. I'm sure culutural convention evolved that into making "left" and "right" general direction indicators.

From a political standpoint, it's amusing that "left" means weak and useless while "right" means strong and ruling.

I always remember political right and left by thinking "the right always thing they are right". (I know, really, both sides would thing that they are right, but I always see the left as more openminded, and therefore, wouldn't always claim to be right... at least not the same way right-wing conservatives would.)

I agree with GP. Isn't that an "Axiom" question? Just as why up is up, down is down, etc.; or, why is walk is walk, run is run (why not call it walkER), no matter which language it is spoken/written. I do not understand Adrianna's question. They are what they are called (or defined) since the time a communication tool (language) was available. And, it is an on going process. There are things being "called/defined" constantly as generation evolves from one to another.

"Right," and its associations with goodness, go back at least to Proto-Indo-European *reg-. Words for "left," on the other hand, have been frequently reinvented. The goodness of "right" probably comes from an interweaving of things: 1. The mjaority of people are right-handed. In a culture which gives a postive value to the common and negative to the uncommon (which is most cultures), right is going to acquire positive value. 2. Proto-Indo-Europeans faced east when they prayed (they "oriented" themselves), because that's where the light comes from. When you do this, the light half of the world is on your right. 3. The celestial objects go from east to west via the south. This is the way you go if you turn to the right. By turning to the right, you follow the cosmic order.<br>

That;s half the question. Why doesn't the Proto-Indo-European word for "left" survive? Because left is bad in Indo-European thought, so the word used for it is bad, so people come up with euphemisms for it, which replace the original word, which is then forgotten. The euphemism then acquires a negative value, and new euphemisms are created, and so on.